Sarcastic, witty or just plain mean…?

When people make continuous sharp remarks that amuse them and other people around and have everyone including yourself laughing while you’re actually cringing and crying on the inside…what exactly is that? Are they doing it to make themselves look good, do they really think its funny or are they just plain mean…? I sarcasm a smart person’s way of joking around or a smart person’a way of being an ass?